1. Field of the Invention
Exemplary embodiments of the present invention relate to an apparatus for adjusting the length of a tension tie for a large deployable antenna, which is a structure based on a cable network; and, more particularly, to an apparatus for adjusting the length of a tension tie for a cable network antenna, which includes a retaining case provided with a plurality of retaining holes and a retainer inserted into one of the retaining holes so that the length can be adjusted precisely at a narrow interval.
2. Description of Related Art
As generally known in the art, a cable network refers to a number of interconnected cables, which are structured and tensioned to form a structure having predetermined rigidity.
FIG. 1 is a schematic perspective view illustrating a deployable antenna made of a cable network, to which the present invention pertains. As illustrated, the deployable antenna 100 made of a cable network includes a front net 110, a rear net 120, and tension ties 130 connecting nodes of the front net 110 with corresponding nodes of the rear net 120.
A rim truss 140 extends along the periphery of the cable structure to support it as a single structure. A conductive mesh 150 is finally attached in the shape of the front net to form a reflective surface of a desired shape. The rim truss 140 is collapsible, i.e. it can be folded into a smaller size, and so are the cable network and the mesh 150. Such an antenna is transported to the space and then deployed to have a diameter of 10m or larger (i.e. circular-aperture paraboloidal antenna).
The function of the tension ties 130 will now be described in detail. The tension ties 130 connect nodes of the front and rear nets to each other. The length of each tension tie is determined based on the height of the paraboloid at the coordinate of each tension tie so that the front and rear nets create symmetric paraboloids. If necessary, the reflective surface may be planar or spherical, instead of paraboloidal. In theory, the length of tension ties for antennas having such construction needs no adjustment. However, errors related to the length of cables, points of connection between respective cables, the overall structural shape of the antenna, etc. necessitate adjustment of the length of tension ties.
Furthermore, tension ties are not very long, which means that it is easy to fabricate tension ties that meat allowed tolerances. Overall structural shape error necessitates tuning of tension tie's length in order to compensate the shape error. The number of tension ties mainly depends on the size of the antenna. Specifically, antennas of about 10 m require hundreds of tension ties. Adjustment of the length of such tension ties require a lot of time and manpower, which eventually increases the product price.
It can be therefore said that the length of tension ties needs to be adjusted easily and rapidly. The amount of adjustment of the length of tension ties is given by measurement of the reflective surface. In order to confirm that the length has been adjusted as desired, the operator needs to easily check the amount of adjusted length by the naked eye.
FIG. 2 is a schematic perspective view illustrating the structure of a conventional tension tie disclosed in U.S. Pat. No. 5,680,145 of Astro Aerospace Corporation. The tension tie includes a spring 202, a spring case 201, a tension tie cable 203, and components 204a and 204b for connecting the tension tie to front and rear nets. This prior art document mentions no method for adjusting the length of the tension tie. It is thought that, according to such structure, the length of the spring increases or decreases in proportion to variation in length of the tension tie so that the length is automatically adjusted. This method may effectively correct the length of only a few local tension ties of the entire antenna. However, if there is an overall deviation of the length of tension ties, it cannot be corrected by the conventional method. More specifically, if an accurate paraboloid fails to be formed on the reflective surface of the front net by tension ties (i.e. if the overall curvature is incorrect), such deviation cannot be corrected automatically. Furthermore, even if a surface has been formed automatically, it is impossible to manually correct a part of it when necessary.
In the end, the spring is assembled while being tensioned to some extent. If the antenna is folded, there is no tension, and friction exits between the spring and the case. The tension tie begins to be tensioned as the folded antenna is deployed. It is not until the tension overcomes the friction between the spring and the case that the length increases up to the assembly length (i.e. final length) so that the desired reflective surface is formed. In other words, insufficient tension may fail to overcome the friction between the spring and the case, deviating from the final length of the tension tie.